The need to protect the kidney during periods of ischemia has been created by the advent of those surgical procedures which, of necessity, interrupt the renal circulation. The most notable of these operations is renal allotransplantation. We have recently accumulated data to show that a single initial perfusion of the totally ischemic canine kidney with a cold hyperosmolar intracellular electrolyte solution can protect the kidney for up to 72 hours when the kidney is stored at 2 degrees centigrade following perfusion. It is proposed to validate and extend the data concerning renal preservation for allotransplantation by performing experiments designed to: (1) Compare the two predominant methods of renal preservation currently in existence, i.e., kidney preservation by initial perfusion and hypothermic storage, vis-a-vis kidney preservation by continuous pulsatile perfusion; and (2) assess the effectiveness of the recently described hyperosmolar intracellular electrolyte solution employed in conjunction with preservation by continuous pulsatile perfusion.